This invention relates to radiant solar energy absorbers as used for example in radiant solar energy concentrating apparatus. The present invention also relates to solar energy concentrating apparatus incorporating such radiant energy absorbers.
In solar energy collecting apparatus, a solar energy absorber is usually provided to absorb solar energy concentrated or collected by the apparatus. In one arrangement, solar energy is concentrated on a absorber in the form of a tubular member which carries an energy transfer medium which may be oil, water or other fluid. To increase radiant energy collection, the absorber may be provided with a selective surface. Alternatively, the absorber may have its exposed surface treated so as to be for example a black surface to increase energy collection and to ensure efficient energy transfer to the energy transfer medium.
Where the tubular absorber carriers an energy transfer medium in the form of water, the water is heated by the concentrated solar energy and may be converted under the influence of the concentrated solar energy into steam for example for driving steam turbines which drive electrical generators for the generation of power
The present invention aims in one aspect to provide a solar energy absorber for use in radiant solar energy concentrating apparatus which has improved energy collection properties for the purposes of the efficient heating of water and/or steam. The present invention in yet a further aspect aims to provide radiant solar energy concentrating apparatus incorporating a solar energy absorber of the above type. The present invention in yet a further aspect aims to provide method for producing superheated steam using solar energy concentrating apparatus incorporating an improved solar energy absorber. Other objects and advantages of the invention will become apparent from the following description.
The present invention thus provides in a first aspect, a solar concentrator absorber tube assembly for receiving and collecting radiant solar energy concentrated by said solar concentrator, said absorber tube assembly comprising a fluid flow absorber tube having an outer surface arranged to be exposed in use to said concentrated solar energy, said surface being provided with a plurality of grooves, said grooves being of substantially V-shaped configuration in cross section, and a helically extending flow passage within said fluid flow tube and adjacent, said outer surface for the passage of water and/or steam through said absorber tube assembly.
Suitably, a longitudinally extending annular space is formed within the tube adjacent the outer surface thereof and the helically extending passage is formed within the annular space. Most suitably, helically extending barrier means are provided within the annular space to define the helically extending flow passage.
The annular space suitably is defined between the wall of the tube and an inner wall or surface spaced radially inwardly of the tube wall, the tube wall including the outer surface which in use is exposed to the concentrated radiant energy. The helically extending barrier means suitably extends from the inner wall to the tube wall.
In one form, the helically extending barrier means is defined by a separate helical separator member or members which may comprise a helically formed wire having a diameter substantially the same as the distance between the inner wall and tube wall.
In an alternative form, the helically extending barrier means may comprise a fin, rib or other member projecting inwardly from the tube wall towards the inner wall. In yet an alternative form, the helical barrier means may comprise a fin, rib or other member on the inner wall which project outwardly towards the tube wall.
The inner wall may comprise the wall of an inner hollow tubular member arranged coaxially within the absorber tube. In this configuration, the inner tubular member may define internally a flow passage for supply of fluid to or for conveying fluid from the helical flow passage. Alternatively, the inner wall may comprise the wall of a solid tubular member
In yet a further arrangement where an inner tubular member is provided, a feed tube may be located coaxially within the inner tubular member, the feed tube being spaced from the inner tubular member to define an air space insulating inward flow from outward flow. Preferably, corresponding inner ends of the inner tubular member and feed tube are interconnected. Preferably also the corresponding outer ends of absorber tube and inner tubular member are interconnected.
Typically, the pitch of the helical barrier means is approximately xc2xd of the diameter of the absorber tube however the pitch may be varied to increase or decrease the cross section of the helical flow passage and therefore decrease or increase the speed of flow of water/steam along the passage. The pitch may also vary along the length of the absorber tube to suit the degree of conversion of water into steam and suit continuous expansion of the steam whilst maintaining optimum Reynolds numbers.
Suitably the grooves in the outer surface of the absorber tube are arranged in a juxtaposed attitude relative to each other and provided substantially over the whole of the exposed surface of the absorber tube.
The grooves suitably comprise grooves which extend circumferentially around the absorber tube transversely relative to the longitudinal axis of the tube. Most suitably, the grooves are defined by a screw thread formed in the exposed surface of the tube. Alternatively, the grooves in the surface exposed to the concentrated solar energy may extend longitudinally and parallel to the longitudinal axis of the absorber tube.
Typically, the included angle of the V-shaped grooves is in the range of 30xc2x0 to 70xc2x0 where the operating temperature is 300xc2x0 C. to 600xc2x0 C. and the absorptivity of the absorber tube is in the range of 70% to 95% and the emissivity of the absorber tube at the operating temperatures referred to above is in the range of 5% to 30%.
The grooves in the outer surface of the absorber tube may be formed by any known process such as by machining or casting.
The present invention also provides solar energy concentrating apparatus including a radiant solar energy absorber tube assembly of the above-described type.
The present invention in yet a further aspect provides a solar energy absorber tube assembly for receiving concentrated solar energy comprising an outer tubular member, said tubular member having an outer surface arranged to be exposed in use to concentrated radiant solar energy, said outer surface being provided with a plurality of grooves, said grooves being of substantially V-shaped configuration in cross section, a first inner tubular member arranged coaxially within said outer tubular member and defining therewith an annular space, a helically extending separator within said annular space and defining a helical flow passage extending along said absorber tube assembly for the passage of water and/or steam, an outlet at one end of said absorber tube assembly communicating with said annular space for outlet flow of water and/or steam from said helical flow passage, and a second inner tubular member arranged coaxially within and spaced from said first inner tubular member, said second inner tubular member communicating with said annular space at the other end of said absorber tube assembly, said second inner tubular member defining an inlet for the flow of water and/or steam to said helical flow passage for flow therethrough to said outlet.
Suitably, the second inner tubular member is fixed at its inner end to the corresponding inner end of the first inner tubular member
Preferably, the second inner, tubular member is free at its outer end so as to be capable of movement upon heat expansion relative to the first inner tubular member.
In yet a further aspect, the present invention provides radiant solar energy concentrating apparatus including a plurality of solar energy absorbers of the above type wherein the outlets of respective solar energy absorbers are connected to the inlet of adjacent solar energy absorbers whereby the solar energy absorbers are arranged in series.
In yet a further aspect, the present invention provides solar energy concentrating apparatus including at least one solar concentrator and an absorber tube assembly for receiving radiant solar energy concentrated by said solar concentrator, said absorber tube assembly comprising a fluid flow absorber tube having an outer surface, said surface being provided with a plurality of grooves, said grooves being of substantially V-shaped configuration in cross section, and a helically extending flow passage within said fluid flow tube and adjacent said outer surface for the passage of water and/or steam through said absorber tube assembly.
Preferably, the absorber tube assembly includes a first inner tubular member arranged coaxially within said absorber tube and defining therewith an annular space, a helical separator in said annular space defining said helically extending flow passage, and a second tubular member arranged coaxially within said first tubular member and spaced therefrom, said second tubular member defining a feed tube for supplying water and/or steam to said helical flow passage.
The present invention in yet a further aspect provides a method of generating superheated steam, said method including the steps of:
providing radiant solar energy concentrating apparatus comprising a plurality of solar energy concentrators, absorber tube assemblies associated with each concentrator to receive concentrated solar energy therefrom, each said absorber tube assembly comprising fluid flow absorber tube having an outer surface, said surface being provided with a plurality of grooves, said grooves being of substantially V-shaped configuration in cross section, and a helically extending flow passage within said fluid flow tube and adjacent said outer surface for the passage of water and/or steam through said absorber tube assembly, said absorber tube assemblies of respective solar energy concentrators being connected in series, and
supplying water to said series of absorber tube assemblies, said water being heated and converted into steam and said steam being heated into superheated steam in passage through respective absorber tube assemblies.